At present, research and development of various display elements are active. Especially, organic electroluminescent (EL) elements can obtain light emission with a high luminance at a low voltage, and therefore, are noticed as a promising display element.
As measures for enhancing characteristics of light emitting elements, there is reported a green light emitting element utilizing light emission from an ortho-metalated iridium complex (Ir(ppy)3:Tris-Ortho-Metalated Complex of Iridium(III) with 2-Phenylpyridine) (see Applied Physics Letters, 75, 4 (1999)). This element attains an external quantum yield of 8%, which is superior to an external quantum yield of 5% that has hitherto been considered to be a limit in conventional elements. However, since this element is still low in efficiency and is limited to green light emission, it is narrow with respect to the range of application as a display. Thus, development of light emitting elements of other colors with a high efficiency has been demanded.
Complexes having a picolinic acid ligand and light emitting elements containing the same are disclosed (for example, see WO 01/41512, WO 02/44189 and WO 02/45466). However, light emitting elements containing a complex that can be driven at a lower voltage and can undergo light emission with a high luminance are demanded.